1. Technical Field
This invention relates to water treatment systems and, more particularly, to a waste water treatment system for use in a rectangular clarifying tank and including plastic buoyant collector flights, integrated bull and drive sprockets, and a chain drive assembly with dual drive shafts.
2. Discussion of Related Art
The use of a water treatment system including a series of scraper or drag flights that are carried and driven by a pair of parallel conveyor chains throughout a rectangular clarifier, i.e. a rectangular concrete settling tank, is generally known in the art. Typically, the conveyor chains are driven by sprockets within the tank. Such a system is commonly employed for removing waste solids such as grit (i.e., non-biodegradable solids such as stones, sand, or glass), sludge and scum from the waste water in the tank. This type of waste water treatment system is commonly used in rectangular clarifying tanks having widths varying from 10 feet to 22 feet. Clarifying tanks of this size are typical for many applications in the United States. An example of such a system for tanks of this size is the waste water treatment system disclosed in commonly assigned U.S. Pat. No. 4,645,598 to Hannum which is hereby incorporated by reference. Generally, the series of flights this system move in one direction partially above the top surface of the waste water for pushing scum into a collector for its removal. Concurrently, other flights in the series move in an opposite direction along the bottom floor of the tank with the front faces of the flights collecting and gathering settled solid waste materials such as sludge. During this process, the flights may be subjected to heavy loads, commonly referred to as sludge loads, that are transferred to the other components of the system including, but not limited to, the conveyor chains, sprockets and drive assembly. In order to reduce the loads on the system's components, substantially all of the working parts are made from non-metallic material which is lightweight, minimizes wear between components, and has a high immunity to the corrosive environment within the clarifying tank.
Many clarifying tanks in the United States and in Europe have widths varying from 22 feet to 26 feet. Historically, the water treatment systems employed in these clarifiers have employ either steel or stainless steel conveyor chains, sprockets, and steel torque tube shafts in conjunction with wooden flights or steel bridge scraper systems. Unfortunately, such systems encounter many problems due to corrosion from the corrosive environment within the tanks as well as excessive wear between components, both of which create maintenance problems. Again, the type of system disclosed in U.S. Pat. No. 4,645,598, with minor modifications, may be used in clarifying tanks of this size in order to overcome such problems.
Typically, as the width of a settling tank is increased, the length a system's flights, as well as other hardware components, must also be correspondingly increased or strengthened for the removal of additional waste solids throughout the tank's additional surface area. A problem associated with simply increasing the length of the flights is that the flights will be subjected to greater sludge loads that may cause excessive center deflection of the flights. Such excessive deflection creates torsional loads as well as simultaneous twisting and bending of the flights that can cause the flights, the flight attachment links and/or other components of the system to fail. Similarly, such deflection often causes the wear shoes of the flights traveling along the top surface of the waste water to drop off return rails causing a potential system failure. Additionally, for many typical systems, as a tank is widened, the system's drive shaft, usually spanning the width of the tank, must also be lengthened. This may cause the drive shaft to deflect or bend due to an increase in its own weight.
In an attempt of overcome such problems, past waste water treatment systems have increased the mass of certain portions of the flights and associated hardware in order to increase the flight's strength, stiffness, and resistance to deflection. However, the increased mass and weight of the flights and associated hardware may create excessive loads that can cause failures of other components within the system.
Such problems are further compounded in rectangular clarifying tanks having widths greater than 26 feet. Many clarifying tanks have widths exceeding 32.8 feet (10 meters). For example, in Europe, many clarifying tanks have widths exceeding 39.36 feet (12 meters) and commonly employ steel bridge scraper systems that experience problems related to rusting and accelerated wear. For tanks of these sizes, the waste water, treatment system disclosed in commonly assigned U.S. Pat. No. 4,810,383 to Hannum, which is hereby incorporated by reference, overcomes the above-discussed problems in a cost effective manner. Briefly, this system employs a suspended cable system which divides the tank into multiple parallel clarifiers without the use of or expense of massive concrete structures required for steel bridge scraper systems.
Unfortunately, the use of this system in many existing rectangular clarifying tanks having widths between 26.24 feet (8 meters) and 35 feet (10.7 meters) may not be cost effective. Additionally, clarifying tanks having widths within this range may be too wide for the waste water treatment system disclosed in U.S. Pat. No. 4,645,598 to Hannum to be effective. Typically, previous waste water treatment systems used in clarifiers Slaving widths within this range, i.e., 8 meters to 10.7 meters, utilize steel conveyor chains, sprockets and sprocket shafts. As discussed above, steel components used in a waste water treatment system have high susceptibility to corrosion from exposure to the corrosive environment within the waste water treatment system during operation and maintenance procedures. In addition, steel components are heavy and prone to excessive wear. This combination of factors reduces the energy efficiency and durability of such steel systems and increases maintenance costs.
It is therefore desirable to provide a waste water treatment system for use in rectangular clarifying tanks having reduced weight for increased efficiency and durability as well as high immunity to corrosion and minimal wear between components.
More particularly, it is desirable to provide a water treatment system with buoyant non-metallic collector flights exhibiting minimal deflection during operation as well as non-metallic flight attachment links, non-metallic integrated bull and drive sprockets and a chain drive assembly with dual drive shafts.
It is further desirable to provide a waste water treatment system for use in a rectangular clarifying tank having a width within the range of 8 meters to 10.7 meters and that has reduced weight, wear and high immunity to corrosion.